Upgrade django-rest-framework version to edX fork, which is DRF v3.6.3

with a custom patch needed by edx-platform.
Upgrade django-filter as well to v1.0.4
Import DjangoFilterBackend from the correct module - django_filter.
Add django-filter to INSTALLED_APPS.

lms/djangoapps/discussion_api/tests/test_views.py

@@ -1,6 +1,8 @@
 """
 Tests for Discussion API views
 """
+from __future__ import unicode_literals
+
 import json
 from datetime import datetime
 from urlparse import urlparse
@@ -376,7 +378,7 @@ class ThreadViewSetListTest(DiscussionAPIViewTestMixin, ModuleStoreTestCase, Pro
             results=expected_threads,
             count=1,
             num_pages=2,
-            next_link="http://testserver/api/discussion/v1/threads/?course_id=x%2Fy%2Fz&page=2",
+            next_link="http://testserver/api/discussion/v1/threads/?course_id=x%2Fy%2Fz&following=&page=2",
             previous_link=None
         )
         expected_response.update({"text_search_rewrite": None})

lms/djangoapps/discussion_api/tests/utils.py

@@ -1,6 +1,8 @@
 """
 Discussion API test utilities
 """
+from __future__ import unicode_literals
+
 import hashlib
 import json
 import re

lms/djangoapps/experiments/views.py

@@ -1,9 +1,9 @@
 from django.contrib.auth import get_user_model
 from django.db import transaction
+from django_filters.rest_framework import DjangoFilterBackend
 from edx_rest_framework_extensions.authentication import JwtAuthentication
 from rest_framework import permissions, viewsets
 from rest_framework.decorators import list_route
-from rest_framework.filters import DjangoFilterBackend
 from rest_framework.response import Response
 
 from experiments import filters, serializers

lms/djangoapps/teams/views.py

@@ -499,7 +499,7 @@ class TeamsListView(ExpandableFieldViewMixin, GenericAPIView):
             return Response(status=status.HTTP_403_FORBIDDEN)
 
         data = request.data.copy()
-        data['course_id'] = course_key
+        data['course_id'] = unicode(course_key)
 
         serializer = CourseTeamCreationSerializer(data=data)
         add_serializer_errors(serializer, data, field_errors)